Fear of deadly attack by lone maverick as officers alert major firms to danger of green extremism

Police have warned of the growing threat of eco-terrorism after revealing they are investigating a group which has supporters who believe that reducing the Earth's population by four-fifths will help to protect the planet.

Officers from a specialist unit dedicated to tackling domestic terrorism are monitoring an eco-movement called Earth First! which has advocates who state that cutting the Earth's population by 80 per cent will ease pressure on other species. Officers are concerned a 'lone maverick' eco-extremist may attempt a terrorist attack aimed at killing large numbers of Britons.

The National Extremism Tactical Co-ordination Unit, which collates intelligence and advice to police forces, has revealed that eco-activists are researching a list of target companies which they believe are major polluters or are exacerbating the threat of climate change.

The unit is currently monitoring blogs and internet traffic connected to a network of UK climate camps and radical environmental movements under the umbrella of Earth First!, which has claimed responsibility for a series of criminal acts in recent months.

A senior source at the unit said it had growing evidence of a threat from eco-activists. 'We have found statements that four-fifths of the human population has to die for other species in the world to survive.

'There are a number of very dedicated individuals out there and they could be dangerous to other people.'

Earth First! says its mission is 'about direct action to halt the destruction of the Earth' and advocates 'civil disobedience and monkeywrenching', tactics that include sabotage and disruptive behaviour. The movement has links to US environmental extremists which have waged a campaign of violence in America, including the firebombing of a string of 4x4 car dealerships in California in 2003 and alleged arson attacks on other property.

The anti-extremist unit has already alerted a number of major companies which have been accused of being carbon polluters with advice on how they can withstand being targeted by eco-terrorists. Companies are thought to include airport operator BAA, an international mining conglomerate BHP Billiton and firms connected to UK coal-fired power stations.